Lung cancer has remained the leading cause of cancer death in the United States and worldwide for many years. The standard diagnostic approach for lung cancer involves a full chest pre-operative computerized tomography (CT) scan followed by sampling of suspected regions of interest (ROIs) through either bronchoscopy or percutaneous needle biopsy. Bronchoscopy is often preferred because it is a minimally invasive procedure with a fast patient recovery period, and it has been recognized as a safe and effective approach for lung cancer diagnosis and staging.
After the CT scan and prior to sampling ROIs using a bronchoscope, a preliminary but critical step is to find a feasible path (way) for the bronchoscope to travel through the patient's bronchial tree and reach a location close enough to the ROIs to perform biopsies. Traditionally, a physician first studies the diagnostic CT scan to detect suspected ROIs. For each ROI, he/she then starts at a location close to the ROI and traces visible cues of the patient's bronchial tree on 2D sectional images, usually axial slices. The cues are pieces of bronchi on 2D images, appearing as elliptical dark regions surrounded by lighter areas (soft-tissue bronchial walls).
Using these visible cues, the physician can reconstruct a feasible path to allow a bronchoscope to travel through the patient's bronchial tree, reach a location close enough to the suspect ROI, and perform a suitable biopsy procedure. However, the physician must reconstruct the paths mentally and memorize each path for individual ROIs before the procedure. As a result, path planning, without computer-aided assistance, can be burdensome for the physician, and it requires rich skills and experience.
With the development of CT and interventional guidance techniques, considerable efforts have been undertaken to develop image-based or electromagnetic-based navigation systems for planning and guiding bronchoscopic procedures (e.g., Broncus LungPoint® Virtual Bronchoscope Navigation System, Superdimension i-logic System™). In these approaches, path planning is integrated into the systems as a vital step prior to real-time guidance of surgical procedures and driven to provide an optimal path or path candidates nearly automatically to reach individual ROIs.
These existing automated approaches require a high-resolution CT scan prior to the bronchoscopic procedure. A powerful segmentation method to extract a full human bronchial tree structure from the CT images, and an intelligent optimum path search process. These requirements are not trivial. A full segmentation of a human bronchial tree structure from a CT scan is difficult and time-consuming. This is especially true when small airway bronchi are involved when dealing with peripheral ROIs. The segmentation requires considerable processing time, and may still require human interaction. Moreover, the segmentation results are highly dependent upon the quality of the pre-operative CT images. Due to the high processing time, these automated approaches are not practical when the patient is on the table.
Even with good bronchial tree segmentation, the optimal path planning approach must also take account for parameters of the endoscope that will be used to reach each ROI in order to generate feasible paths. The parameters of the endoscope, however, may not be available at the time that path planning is performed, and the physician may change endoscopes during the procedure.
Automated path planning approaches will usually result in multiple path candidates, and the physician will have to study each candidate and chose a feasible path from among the candidates. Some times none of the candidates will be a feasible path, and the physician will need to rely on his/her experience, instead of following the chosen path. Also, the generation of multiple path candidates represents a significant processing burden.
Thus, the automated path planning approaches: (1) may not be available when there is not sufficient data (e.g., high resolution CT and endoscope parameters); (2) are not feasible for on-the-table diagnosis and planning, which is preferred in most real clinical applications; (3) may not be necessary because a bronchoscopic procedure is often performed to deal with one to three ROIs, and the physician may prefer to rely on the bronchial cues plan a path for the procedure; and (4) may provide multiple or unreliable paths.